The Siskin III’s great claim to importance is that it was one of the first fighters with an all-metal structure to enter RAF service. Where the fighters of the First World War were built of wood and wire, the Siskin III had a framework built from steel and light alloy — still covered in fabric, in the fashion of the day, but fundamentally a metal aeroplane.

This mattered because wood had real drawbacks: it warped, its glued joints deteriorated, and airframes could rot in damp or tropical conditions. A metal structure was more durable, more consistent and easier to maintain, and far better suited to a peacetime air force that needed its aircraft to last. The Air Ministry encouraged the switch to metal in the early 1920s, and the Siskin was one of the aircraft that led it.

The Siskin began just after the First World War as a design by the Siddeley-Deasy company, which was absorbed into Armstrong Whitworth. The earliest Siskins of around 1919 had conventional wooden structures, like the wartime fighters they were meant to succeed.

The decisive change came in the early 1920s, when the design was reworked around a metal structure to become the Siskin III. It was this metal-structured version that the RAF adopted from 1924, and it is the Siskin III and its successor the IIIA that matter historically — the point at which a promising wooden design was transformed into a pioneering metal one.

The Siskin was a single-seat sesquiplane — a biplane whose lower wing was much smaller than the upper. The slender lower wing carried distinctive broad vee-form interplane struts up to the main upper wing, giving the aircraft its characteristic appearance.

Power came from the Armstrong Siddeley Jaguar, an air-cooled radial engine — itself a forward-looking choice when many fighters still used liquid-cooled inline engines. The combination of a compact radial and a light, strong metal structure gave the Siskin lively performance and, above all, the superb agility that made it such a fine display aircraft.

The definitive version of the type was the Siskin IIIA, which appeared in the mid-1920s. It introduced a more powerful, supercharged version of the Jaguar engine and various detail refinements, and it was significantly more capable than the earlier Siskin III.

It was the IIIA that became the true mainstay of the type, equipping a large number of RAF home-defence fighter squadrons through the second half of the 1920s and into the early 1930s. For several years it was one of the backbones of Britain’s air defence, and it accounts for the majority of the four hundred and fifty or more Siskins built.

The 1920s and early 1930s were the golden age of the RAF air pageants at Hendon — spectacular annual public displays that drew enormous crowds and were a highlight of the London social calendar. In the long peace between the wars, these pageants kept the RAF in the public eye and showcased the skill of its pilots.

The agile Siskin was one of the stars of these displays. Siskin squadrons performed dazzling formation aerobatics that thrilled the crowds, and the type became one of the emblematic aircraft of the interwar RAF’s confident public face. To picture RAF fighters looping over Hendon in the 1920s is very often to picture Siskins.

The Siskin is especially remembered for one extraordinary feat: “tied-together” formation aerobatics. Whole formations of Siskins would fly loops and rolls with their wingtips literally connected by lengths of elastic cord or light rope, staying joined throughout the manoeuvres.

It was a breathtaking display of precision flying, demanding perfect coordination and superb handling, and it became one of the signature spectacles of the Hendon era. Squadrons such as No. 43, the famous “Fighting Cocks,” built their reputations on such displays. Few images better capture the daring and showmanship of the interwar RAF.

The Siskin also served across the Atlantic. The Royal Canadian Air Force adopted the type and operated Siskins as front-line fighters into the 1930s; for a time the Siskin was one of the RCAF’s principal fighter aircraft, a significant type for a young and growing air force.

The Canadians, like the RAF, formed a celebrated Siskin aerobatic team, and they flew the type through the demanding Canadian climate, including fitted with skis for winter operations from snow. The Siskin’s rugged, all-metal structure made it well suited to these conditions, and its Canadian service is an important part of the type’s story.

Alongside the single-seat fighters, the Siskin was also built in a two-seat dual-control trainer version. This allowed pilots to be converted onto the type under instruction, and gave training units a Siskin of their own for conversion and continuation flying.

A trainer variant of this kind was typical of a successful interwar fighter, and it extended the Siskin’s usefulness beyond the front-line squadrons into the training role. It is a reminder that a service aircraft of the period was usually a small family of related types rather than a single model.

The Siskin was armed, in the standard fashion of the period, with two fixed, forward-firing Vickers .303-inch machine guns synchronised to fire through the propeller arc. This was the near-universal fighter armament of the 1920s, and it remained standard in the RAF for many years.

Performance was modest by later standards but respectable for its day: a top speed of somewhere around 150 to 156 mph and a good rate of climb and ceiling, thanks to the supercharged Jaguar of the IIIA. What really distinguished the Siskin, though, was not raw speed but agility — the light, strong metal structure and radial engine gave it the handling that made it such a superb aerobatic mount.

The Siskin’s front-line career was relatively short, because fighter development, though slower than it would later become, was still relentless. From the late 1920s newer designs began to replace it in RAF service — above all the Bristol Bulldog, which took over much of the home-defence role at the turn of the decade.

The Bulldog was followed by the Gloster Gauntlet and Gladiator, and ultimately by the monoplane Hurricane and Spitfire. The Siskin was progressively withdrawn from front-line service in the early 1930s, having done its job: it had helped carry the RAF through the transition to metal construction and had served as a reliable mainstay for the better part of a decade.

Unlike many aircraft in this collection, the Siskin never fought a war. It was designed, built and flown entirely in the long peace between 1918 and 1939, and by the time the Second World War came it had long since left front-line service. It has, therefore, no combat record to speak of.

This is not a mark against it but simply a fact of its timing. The Siskin’s importance lies elsewhere — in its pioneering metal structure and in its role as one of the defining fighters and display aircraft of the interwar RAF. It is a reminder that an aircraft can matter a great deal without ever firing its guns in anger.

The Armstrong Whitworth Siskin sits at an important hinge in the history of the fighter aeroplane. Behind it lay the wooden biplanes of the First World War; ahead lay the all-metal, stressed-skin monoplanes of the Second. The Siskin, with its metal framework under a fabric skin and its air-cooled radial engine, was a genuine step along that road.

It proved, in everyday squadron service and in the glare of the Hendon pageants, that a metal-structured fighter was durable, practical and effective. In doing so it helped ease the RAF’s transition from the wooden age to the metal one — a quiet but genuine contribution to the development of the modern fighter.

The important Siskins were the metal-structured versions. The Siskin III entered RAF service in 1924 as one of the first all-metal-structured fighters in the service. The Siskin IIIA followed in the mid-1920s with a more powerful supercharged Jaguar engine and refinements, and became the definitive and most numerous version.

Alongside the single-seat fighters was a two-seat dual-control trainer version for conversion and instruction. Earlier, wooden-structured Siskins had existed from around 1919, but it is the metal Siskin III and IIIA that matter historically. Together the family accounts for something over four hundred and fifty aircraft.

As with most RAF aircraft of the 1920s, there is no reliable, transparent public figure for the Siskin’s unit cost, cost per flight hour or total programme cost. It was procured across several years under the tight defence budgets of the period, and consistent lifetime cost data does not survive in a usable, comparable form.

Rather than repeat an invented number, we list the cost fields here as “not reliably recorded.” As a compact single-engined biplane of metal-and-fabric construction, the Siskin would have been relatively economical, which helped the RAF field it in useful numbers as a mainstay home-defence fighter during the lean interwar years.

The Siskin’s importance rests on two things. First, it was one of the first all-metal-structured fighters to enter RAF service, helping carry the service from the wooden aeroplanes of the First World War towards the all-metal fighters of the future — a genuine technological milestone. Second, it was one of the principal RAF fighters of the 1920s and one of the defining aircraft of the great age of air displays.

That it never saw combat does not diminish this. The Siskin’s significance is that of a pioneer and a mainstay: an aircraft that proved metal construction in everyday service and that gave the interwar RAF one of its most enduring public images, looping over the crowds at Hendon.

A small number of Armstrong Whitworth Siskins survive, reflecting the type’s service on both sides of the Atlantic. An example is preserved in the collection of the Royal Air Force Museum in Britain, and another at the Canada Aviation and Space Museum, recalling the type’s RCAF service.

Given how few interwar fighters were preserved — most were scrapped once obsolete, long before anyone thought them worth saving — these survivors are precious. They are rare tangible links to a pioneering aircraft that helped bring the fighter out of the wooden age and that thrilled the crowds of aviation’s golden age.